This invention relates generally to manufacturing and, more particularly, to printed circuit boards (PCBs).
A printed circuit board (PCB) (also referred to as a printed wiring board (PWB), or a PC Larninate (PC Lam)) provides a mechanism for implementing a circuit design (i.e., the interconnection of electrical devices and components). A PCB may be xe2x80x9csingle layer,xe2x80x9d xe2x80x9cdouble layer,xe2x80x9d or xe2x80x9cmulti-layerxe2x80x9dxe2x80x94each of which refers to the number of electrically conductive layers. A multi-layer board comprises alternating layers of conductive material and electrically insulating material bonded together. (As used herein, terms of the form xe2x80x9cconductivexe2x80x9d and xe2x80x9cinsulatingxe2x80x9d refer to the properties of electrical conduction and electrical insulation, respectively.)
In order to connect signal paths from one conductive layer to another conductive layer, holes (or through-holes) are drilled through a PCB and are subsequently coated, or plated, with a conductive substance (there are a variety of known techniques for through-hole-plating). These plated-through-holes are also referred to as xe2x80x9cvias.xe2x80x9d In high-density circuit designs, the number of componentsxe2x80x94and the resulting signal paths interconnecting the componentsxe2x80x94typically require use of multi-layer boards with thousands of vias. (It should be noted that there are also other types of holes drilled into a PCB, e.g., xe2x80x9ccomponent holesxe2x80x9d for receiving the pins of a surface mount component.)
Each through-hole comprises a length (which corresponds to the thickness of the PCB across all of the layers) and a diameter. In general, in order to plate the through-hole, the through-hole must have a minimum diameter that is a direct function of the thickness of the PCB, which itself is determined as a function of the design of each layer. (Layers do not have to be the same thickness, and can vary in thickness as a function of the electrical characteristics desired. In addition, this minimum through-hole diameter may also be a function of the particular plating technique, which is not described herein.)
Obviously, the design of a PCBxe2x80x94and the number of conductive layers to usexe2x80x94is directly influenced by the particular circuit design. However, we have also observed that as the decision is made to increase the thickness of the PCBxe2x80x94there may be a concomitant increase in the amount of space, i.e., the minimum diameter, required by through-holesxe2x80x94space that cannot be used to route signals.
Therefore, and in accordance with the invention, instead of coating, or plating a through-hole with a conductive material to form a viaxe2x80x94the via is formed by placing a conductive stake in the through-hole for electrically coupling foils disposed on at least two electrically conductive layers together. Thus, as the thickness of a PCB increases, the diameter of the individual through-holes stay the same and the amount of space taken up by through-holes does not change.
In an embodiment of the invention, a conductive stake is inserted into a through-hole of a PCB for the purpose of forming a via. The conductive stake comprises, e.g., a phosphor bronze material, and is gold-over-nickel plated. The length of the conductive stake is at least as long as the distance between two conductive layers of the PCB. A diameter of the conductive stake is approximately greater than, or equal to, the diameter of the through-hole.